Electronic circuit for triggering stroboscopic devices



Sept. 21V, 19478.

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Sept- 21, 1948 c. M. HATHAWAY 2,449,551

ELECTRONIC CIRCUIT FOR TRIGGERING STROBOSCOPIC DEVICES Original Filed June 11. 1942 2 Sheets-Sheet 2 Patented Sept. 21, 1948 ELECTRONIC CIRCUIT FOR TRIGGERING STROBOSCOPIC DEVICES i `Claude M. Hathaway, Denver, Colo., assigner` to MarcellusS. Merrill, Denver, Colo.

Continuation of application Serial No. 446,611,`

June 11, 1942. Thsapplication Serial No. 653,511

March 11, 1946,

s claims.' (c1. 315-194) This invention relates to a new and improved electronic circuit, and more particularly to a circuit adapted to modify asinusoidal wave form so aste provide a single sharply peaked impulse at a definite pointin each cycle.

This application isV a continuation of my application Serial Number 446,6l1,`filed Junell, 1942, now abandoned.` i i i While circuits of this character are useful for a number of purposes, such circuit is especially desirable for use in connection with a wheel balancing apparatus` and method such as disclosed in my application Serial Number 350,366, filed July 27, 1940, jointly `with Marcellus S. Merrill, which issued August 2l, 1945, as Patent No. 2,383,- 405, and was copending with my application Serial Number 446,611. y

Apparatus for balancing wheels or other rotating bodies comprises essentially means for locating thel unbalanced weight and determining `its amount. This involves, as further steps, the check of the rotating body after the application of corrective measures, such as the additionof localized weight, to determine lWhether -a condition of` bal-` ance has been reached.

This apparatus described in the `previous application comprises means adapted to engage the support for the rotating body and to generate an alternating current having a definite phase relationship with the vibration of the supportv due to the unbalance of the rotating body. The current amplitude is also approximately proportional to 'the amount of unbalance. The apparatus also includes an electronic circuit which "modies the alternatingcurrent wave form to produce a single sharp peak occurring once in each cycle, this peak being utilized to re a strobotron tube. Due to the known and predetermined relationship of the firing instant of sthe tube, with the direction of vibration ofthe unbalanced body at that instant, thelocus of the unbalanced weight is determined by al observation. The approximate amount of the unbalanced weight is determined by a measurement of the current generated by the vibration. y

The present invention relates to an electronic circuit for modifying a sinusoidal wave form` to provide a single peak during Teach cycle, this peak being utilized to re a strobotron tube.

Itis `an object of the present invention` rtoprovide a new and` improved electronic circuit for modifying the `wave form of an alternatingcur-` rent.A -1 j` I U- i. `ltis anotherobjectto provide `an outputwave 2 form having a `single sharp peak for each cycle of the input current. i

It is also an object to provide a circuit in which the output peak has a definite and substantially ixed relationship to the phase of the input sinusoidal `Wave form. Y, Y i

Itis anaddtional object to provide a circuit which requires but few parts, which operates upon a relatively small input current, and which requires only a small amount of power.

It isa further object to provide a circuit which requires apparatus simple in design and operation and-adapted for commercial production and use.

Other and further objects will appear as the description proceeds.`

I have shown the circuit and the Wave forms produced thereby somewhat diagrammatically in the drawings, in which Figure 1 is a block diagram of thecircuit;

`Figure 2 is a schematic circuit diagram;

Figure 3 shows the theoretical Wave forms at different points in the circuit; and

` Figure 4 is similar to Figure 3, but shows the actual -wave 4forms produced, as` observed upon an oscilloscope. e i

y As shown in Figure l, the circuit comprises a pick-up for the current generated by the vibration `due to unbalanced weight, the pickup feeding into a rectier'which blocks half the cycle;

and the passed current is then modified by successivediferentiatorcircuits to give the desired sharply defined and deilnitely located peak which is desired for firing the strobotron tube.

A typical circuit is shown schematically in Figure 2. The meter I I is shownconnected to pickup coil I2 through rectifier network I3, the meter being shunted by the variable resistance I 4. This meter circuit has its pickup coil adjacent the current generating unit. The generating unit A is shown las comprising a pair of iron cores I5, about which arejwound the pickup coils I2 of the meter circuit and also the pickup coil I6 of the strobotron circuit. A permanent magnet I'I is l movably supported adjacent the cores I5 and is connected to a contact member 48 which is adapted to be maintained in contact with a vibratingmember such as afwheel axle orbrake backing plate. Vibration transmitted from the unbalanced rotating member serves to move the magnet I1 toward and away from the cores I5. The relative m-ovement between the parts generates a current having a cycle dependent `upon the periodicity of Vibration and an amplitude` related to the amplitude of vibration. The meter circuit is` independent of the strobotron ring circuit, except that both circuits have pickup coils coupled inductively to the same current generating device.

The mechanical details of construction of the pickup member form no pant of the present invention and Will not be further described herein. A suitable construction is disclosed in my prior joint application referred to above.

The strobotron firing circuit comprises the pickup coil it, which supplies a voltage to the rectier B. The specific form of rectiiiershcwn comprises half of a double diode tube, such as a reverse of that shown in Figure 3. 'The resistor 26 and the capacitor 25 constitute a differentiating circuit, so that the Voltage applied to the control grid 24 of the GSK? tube will be proportional to the slope of d and is shown at e of Figure 3. The theoretical current in the plate circuit of the 6SK7 tube is the negative of this,

Vand is in the form shown at f of Figure 3. The

transformer 33, constitutes a second diiTerentia- GHG, the connection being to the cathode 18.

The rectier plate I9 feeds the half cycle passed through the rectifier to .the `grid 2li of a triode such as a 6J5. The grid circuit includes the grid resistor 2| and the grid capacitor 22 constituting means for modifying the Wave form due to the capacitor 22 charging on the wave front and discharging expcnentially through the resistor 2 l.

The plate 23 of the triode is connected b-y the first diiferentiator circuit vC tothe control grid 2li of a tube such as a GSK'?, as shown. The difierentiator circuit C comprises the'ca'pacito'r 25 and the resistance 26. The plate circuit 'of the triode plate 23 includes the resistance '21 and 'condenser 28. The triode plate is connected through the voltage Adropping resistor 31 to the positive side of the power supply D, which is shown as of conventional form with full Wave rectification.

Y The GSK? tube has its screen grid A2&1 connected through a voltage dropping resistor 30 to the power supply D. The screen grid 29 is also grounded through the voltage regulator tube 38.

The plate 3l of this tubeisconnect'ed to the primary 32 of the coupling transformer 33.` The plate resistance of the tube and the inductance of the transformer primary constitute a second dii"a ferentiato'r circuit.

The secondary 3! 'of the transformer 33 visrconnected across the rectifier 35, which is shown as the second half of the GHG tube used as-the origi nal input rectier, and `which eliminates unwanted reverse peaks of the trigger voltage. The cathode of this rectifier unit is connected to the control grid 36 of the strobotron tube, the voltage supplied serving to trigger the strobctron. Associated with the lstrobotron is a capacitor lill adapted to discharge through the strobotron when the latter is rendered conductive Iand connected across its plate and cathode and a resistor (l2 through which the capacitor is charged.

The theoretical Wave forms are shown in Figure 3 and the actual wave forms produced in the circuit are shown in Figure 4.

Referring lirst to Figure 3, the voltage 'generated by the pickup is assumed to be sinusoidal in form, as shown in c. The voltage, in order that the final trigger peak may occur in the desired phase relation to the vibration force, should be another sinusoid displaced 90 degrees in phase from the input Wave as shown in Figure 3h, which shift can Vbe accomplished, by an integrating circuit `or by the pickup and input circuit, as explained hereafter. This Wave is applied to the rectifier B, shown in Figure 2, and since this rectifier cannot conduct in the forward direction, lthe positive half-cycles will be eliminated, and the voltage applied to the grid of the triode 6J5 will theoretically be as shown .in C' of Figure 3. 1

The voltage which appears 'across thel resistor 27 in the plate circuitL of the ytube will take the wave form shown in d off' Figure 3, being the tor. The voltage across the transformer primary isl therefore proportional to the slope f of Figure 3, 'and theoretically takes the form shown at y of Figure 3. The wave form of h of Figure 3 `Ais reverse of that shown at g of Figure 3 and appears theortically at the control grid of the strobotron tube, after the diode limiting action of the rectifier section 35. It is apparent that if the theoretical Wave forms of Figure 3 actually appeared in the circuit, the strobotron would fire twice in each cycle, and therefore the operation would be unsatisfactory. Y Certain practical limitations, however, intervene to modify the Vactual 'Wave formand 'remedy this defect. Fortunately, these practical modifications result in a 'Wave forin having 'a single sharp peak in each cycle, and th'uspiovide a Wave form suitable for actual operation of astrcbotron. lIn Figure 4 the actual wave yforms in the circuit are shown, these Wave forms being observed an oscilloscope connected te the circuit at the various points. The actual sinusoidal 'Wave of Figure 4a, is similar to the theoretical Wave,

' and the same is true of the phase shifted Wave of Figure 4h. Theoretically it Wiiuld be necesasary to provide an integrating circuit totalise this phase shift, but it has been Afinir-auxin practice that the inductive and capacitive 'reactance ofthe pickup coils and .the distributed selfrapac-v ity of the coils and associated circuit are as to inherently provide the desired integration and phase shift. When 'we reach the Wave form of Figure 4c, however, which is that in the output circuit of the rectifier B, the theoretical curve suffers certain distortions. The discontinuities at the points 4l, 42 'and 43 of Figure 3c are sharp, but the actual circuit, as shown at 44, 45 'and 46, these are slightly rounded.

In order to obtain theV theoretical sha-rp con nersthe rectifier B would have to 'change from infinite conductance for the smallest positive voltage to lnnite resistance for the smallest negative voltage. The corners on the rising volt age are similarly rounded as shown at '45. This is due to the finite time constant of the modify ingirneans including the `plate resistorl` and the grid? capacitance 22, which latter may be in creased by the addition of an extra capacitor' to increase this effect. The wave form of Figure 4d is `the reverse of- Figure 4c. The remaining Wave forms, Figure 4c, f, gV and h, are obtained as before, and it is seen that the actual Wave formhas one sharp positive peak, occurring at a definite time and in fixed Vrelationship to the phase of vthe input sinusoidal wave. The voltage of the sharp positive' peak is suiiicient to lfire the strobotron.

It'will be noted that 'the circuit is; a waveform shaping circuitarld not an amplifying circuit. The original voltage generated by vibrationof the pickup is small, especially if the rotating body is only slightly out of balance. Itis necessary to amplify this Voltage to provlde'for voltage sunlcent to counterbalance the losses in the difiereritiator circuits. It is also necessary to provide theA fnalwave formata voltage such that the sharp peak will' be adequate to `trigger the strobof-` tron.,4 l, nl t `While inthe drawings I haveshown certain embodiments of my .invention, it will be understoodthat itlmay be varied to meet differing conditions andrequirements; and I contemplate such modifications as come within the spiritand scope of the appended claims. l A

What I claimis: l

1. An electronic circuit for generating sharply defined impulses from sine wave currents, including in combination, a rectifier for rectifying the sine wave currents and having an output circuit, an amplifier including a thermionic tube having a grid coupledwtoY the output circuit of the rectifier, means included in said output circuit for modifying `the Wave shape of `the rectified currents,` a second amplifierincluding another therrnionietube having a,plate, coupling means between said tubes including means for differentiating the rectified and modified currents to produce a wave shape having a single peak per cycle in definite phase relation with the sine wave currents, a coupling transformer having primary and secondary windings, said second thermionic tube having a plate circuit including the primary winding of said coupling transformer, saidplate circuit forming another differentiating circuit for more sharply peaking said wave shape, a second rectifier connected in parallel with said secondary winding of said coupling transformer and having an output circuit, and an output circuit electrically coupled to the output circuit of said second rectifier.

2. In an electronic circuit for a stroboscopic device, the combination with electromagnetic pickup means for generating an alternating current of substantially sinusoidal wave form, of an input circuit connecting with the said electromagnetic pickup means for displacing the phase angle of said wave, a rectifier for rectifying the phase shifted wave, an amplifier including a thermionic tube having a grid coupled to the output circuit of the rectifier, means included in said output circuit for modifying the Wave shape of the rectied currents, a second amplifier including another thermionic tube, coupling means between said tubes including means for differentiating the rectified and modified currents to produce a Wave shape having a single peak per cycle in definite phase relation with the phase shifted Wave, a coupling transformer having primary and secondary windings, said second thermionic tube having a plate circuit including the primary winding of said coupling transformer, said plate circuit forming another differentiating circuit, a second rectier connected in parallel with the secondary winding of said coupling transformer, and means for electrically coupling a stroboscopic device to said second rectier.

3. In an electronic circuit for triggering a stroboscopic device, the combination with electromagnetic pickup means for generating an alternating current of substantially sinusoidal wave form, of an input circuit connecting with said electromagnetic pickup means for phase shifting said Wave substantially 90 degrees, a rectifier for rectifying the phase shifted Wave, an amplifier including a thermionic tube having a grid coupled with the output circuit of the rectifier, means included in said output circuit for modifying the shape of the rectied wave, a second amplifier including another thermionic tube, coupling means between said tubes including means for differentiating the rectified and modified currents to produce-"a Wave shape having a single peak per cycle in deflnitefphase relation with the phase shifted wave, a couplingtransformer having primary and secondary windings, said second thermionic tube having 'a plate circuit including the primary winding. `of said coupling transformer, said plate L circuit forming another differentiating circuityand an output circuit electrically coupledwith.thesecondary winding of said coupling transformer, for deriving therefrom currents lhavingfvoltage` impulses capable, of` triggering the stroboscopicdevice. l l l 4m-In :an electronic circuit `for triggering a stroboscopic device,` `an input circuit for supply` ing sine `wave currents, a rectifier for rectifying the sine wave currents, alternateamplifying and differentiating stages for amplifying and differentiating ,said rectified currents, each amplifying stage includingvathermionic tube, the first tube including a control grid and the last tube a plate, means coupling said grid of the first tube with the output of the rectifier, a coupling transformer having a primary winding in the plate circuit of the last tube and a secondary winding, whereby a high Voltage impulse is produced for each cycle of the input sine wave, a second rectifier having an output circuit and connected in parallel with the secondary winding of said coupling transformer, and an output circuit coupled to the output circuit of said second rectifier to `derive currents therefrom having voltage impulses capable of triggering the stroboscopic device.

5. In an electronic circuit for triggering a stroboscopic device, in combination, an input circuit for supplying sine wave currents, a rectifier for rectifying said sine wave currents, amplifying stages each including a thermionic tube, the tube of the first stage including a grid coupled with the output of the rectifier and the tube of the last stage including a plate circuit, a coupling transformer having a secondary winding and a primary winding in the plate circuit of the tube of the last stage, said plate circuit providing differentiating means for Wave shaping the rectified and amplified currents to produce a shape having a, single peak per cycle, whereby a high voltage impulse is produced across the primary winding for each cycle and which has a definite phase relation with said input sine wave, and an output circuit having electrical connection with the secondary winding of said coupling transformer to derive currents therefrom having voltage impulses capable of triggering the stroboscopic` device.

6. An electronic circuit as defined by claim 5, additionally including a second rectier located in the output circuit and connected in parallel with the secondary winding of the coupling trans` former, said second rectifier serving to substantially eliminate unwanted reverse peaks in the shaped wave.

7. In an electronic circuit for triggering a stroboscopic device in definite phase relation with alternating current of substantially sinusoidal Wave form, the combination including, rectifying means supplied with the alternating current for providing current of one polarity, and means coupled to said rectifying means for supplying triggering impulses to the stroboscopic device for each cycle of the input wave and in definite phase relation thereto, said last mentioned means including a first amplifying and diiferentiating stage comprising a thermionic tube having an input circuit coupled to said rectifying means and diifereritiat iiipt icircuit Acoupled 'to said iti'fyinmens and zo 2,3853397 CLAUDE M. HATHAWAYQ REFERENGES CITED V"limi foilwing reiren'ces are ai re'cbrd in the file of this patrlt: Y STATES? iiif Number. Name i 13a-ta m1335611 Nit 1 -v aiuti. 3b; 1940 2,341,541 @prierr :Flats 15,1914

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